This invention relates to the teeming of molten metal. More particularly, it relates to a method and apparatus for determining the weight of molten slag on a bath of molten steel to be teemed into either ingot molds or a continuous casting machine.
When a heat of steel is tapped, from a basic oxygen furnace, for example, the furnace operator cannot prevent a small quantity of slag from passing from the furnace into the teeming ladle. At present, many teeming ladles are provided with weight indicators showing the weight of the ladle contents, viz., the molten steel and the molten slag floating on the molten steel. Without knowing the weight of the steel alone, it is difficult to teem a heat of steel without either pouring some slag into the last ingot mold, thereby producing a "slag top" ingot, or producing an unusable ingot butt.
Slabs of steel rolled from slag top ingots may require special testing before further processing. In addition, such slabs require up to an additional 15% or more discard at the slabbing mill shear. Slag top ingots cause accelerated mold deterioration. In some cases, slag top ingots cannot be removed from the mold by the ordinary stripping process, and the mold must be destroyed to obtain the ingot.
The last ingot poured, known as the ingot butt, must be a minimum height, e.g., 65 to 70 inches, if it is to be rolled into a slab. Shorter ingot butts must be scrapped, resulting in a serious loss in yield.
If the weight of the steel in the ladle were accurately known, it would be possible to decrease the frequency of slag top ingots. In addition, the number of unrollable ingot butts could be reduced by distributing the steel ordinarily used for the butt among the last three or four ingots poured.
It is an object of this invention to provide a method and an apparatus for determining the weight of the molten slag on a bath of molten metal. From this determination, the weight of the molten metal itself can easily be determined.